Niemann-Pick type C (NPC) is an autosomal recessive lipid storage disorder that is characterized by psychomotor retardation, psychosis, cerebellar ataxia with extrapyramidal manifestations, supranuclear vertical opthalmoplegia, seizures, hepatosplenomegaly and foamy cells in the bone marrow. Genetic linkage analysis has linked the NPC gene to the pericentromeric region of human chromosome 18. We have further refined the location of the gene to the subchromosomal band 18q11-q12, between markers D18S44 and D18S480. This interval has been contigged in YACs and BACs clones. We are employing a concerted effort involving positional cloning strategies that takes advantage of the 1) rapid generation of a mouse genetic map that is easily integratable to the human physical mapping efforts, 2) the introduction of YACs into NPC rodent and human cells to assess for complementation by cholesterol esterification impairment and Filipin staining, and 3) the utilization of the information from the mouse genetic map and the YAC complementation to narrow down the candidate interval for the identification of candidate genes part of the positional cloning efforts. Evolutionarily conserved cDNA sequences will then be used to integrate the mouse map with the human map in an attempt to further narrow down the interval. Candidate genes have been isolated using both internal and 3' terminal exon trapping. These clones and additional ESTs mapped to this region will be tested for their ability to complement NPC cells and to search for the molecular lesion in NPC patient cell lines by SSCP and Northern blot analyses.